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1. The highest degree of quality or purity in diamonds or pearls.
2. The foremost rank or quality: a pianist of the first water.
[Probably translation of Arabic mā', water, water luster.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
1. (Jewellery) the finest quality of diamond or other precious stone
2. the highest grade or best quality
3. the most extreme kind: a fool of the first water.
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
1. (formerly) the highest degree of fineness in a diamond or other precious stone. Compare water (def. 13).
2. the finest quality; highest rank.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.